Impact of Soil Sorption Characteristics and Bedrock Composition on Phosphorus Concentrations in two Bohemian Forest Lakes

Abstract

Phosphate (PO4-P) sorption characteristics of soils and bedrock composition were determined in catchments of two mountain lakes, Plesne Lake (PL) and Certovo Lake (CT), situated in the Bohemian Forest (Czech Republic). The aim was to explain higher terrestrial P export to mesotrophic PL compared to oligotrophic CT. Concentrations of Al and Fe oxides were the dominant parameters affecting soil ability to adsorb PO4-P. Depending on concentrations of Al and Fe oxides, P sorption maxima varied from 9.7 to 70.5 mmol kg−1 and from 7.4 to 121 mmol kg−1 in organic and mineral soil horizons, respectively. The catchment weighted mean PO4-P sorption capacity was 3.4 mol m−2 and 11.9 mol m−2 in the PL and CT soils, respectively. The higher PO4-P sorption capacity in the CT catchment was predominantly associated with higher pools of soil and Fe oxides. The CT bedrock (mica schist) released one order of magnitude less P than the PL bedrock (granite) within a pH range of catchment soils (pHCaCl2 of 2.5–4.5). The higher ability of PL bedrock to release P and the lower ability of PL soils to adsorb PO4-P thus contributed to the higher terrestrial P loading of this lake.